Revert r17907 - Make it possible to add more than one piece of embedder data to isolates

Revert r17907 - Make it possible to add more than one piece of embedder data to isolates

> This will allow for using gin and blink bindings in the same process
>
> BUG=317398
> R=svenpanne@chromium.org, dcarney@chromium.org
> LOG=y
>
> Review URL: https://codereview.chromium.org/77913003

BUG=none
R=svenpanne@chromium.org
TBR=svenpanne@chromium.org
LOG=n

Committed: https://code.google.com/p/v8/source/detail?r=17915

[Sven Panne, 2013-11-20 11:55:53]

LGTM. (Cause for the revert: Alignment problems, right?)

[jochen (gone - plz use gerrit), 2013-11-20 12:05:52]

Committed patchset #1 manually as r17915.

[jochen (gone - plz use gerrit), 2013-11-20 12:06:39]

right. the class Isolate appears to be aligned differently on different
platforms :-/